Loss of Efficacy in Ventral Intermediate Nucleus Stimulation for Essential Tremor

The primary aim of this study is report long-term outcomes associate with deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) performed at our institution. We further aimed to elicit the factors associated with loss of efficacy, and to discuss the need for exploring and establishing reliable rescue targets. To study long-term outcomes, we performed a retrospective chart review and extracted tremor scores of forty-three patients who underwent VIM DBS lead implantation for ET at our center. We further evaluated factors that could influence outcomes over time, including demographics, body mass index, duration of follow-up, degree of parenchymal atrophy indexed by the global cortical atrophy scale, and third ventricular width. In this cohort, tremor scores on the latest follow-up (median 52.7 months) were noted to be worse than initial postoperative scores in 56% of DBS leads. Furthermore, 14% of leads were associated with clinically significant loss of benefit. Factors including the length of time since the lead implantation, age at the time of surgery, sex, body mass index, pre-operative atrophy, and third ventricular width were not predictive of long-term outcomes. Our study identified a substantial subgroup of VIM-DBS patient who experienced a gradual decline in treatment efficacy over time. We propose that this phenomenon can be attributed primarily to habituation and disease progression. Furthermore, we discuss the need to establish reliable and effective rescue targets for this sub-population of patients, with ventral-oralis complex (Vo) and dentate nucleus (Dn) emerging as potential candidates.